It allowed him to realize that the mass of an atom is concentrated at its center because the atoms mostly went through the foil but some were deflected. He also realized that an atom probably wasn't just empty space and scattered electron and it had a positive center.
Rutherford's Gold Foil Experiment proved the existence of a small massive center to atoms, which would later be known as the nucleus of an atom. Ernest Rutherford, Hans Geiger, and Ernest Marsden carried out their Gold Foil Experiment to observe the effect of alpha particles on the matter.
Most of the space inside the atom is empty because most of the α-particles passed through the gold foil without getting deflected. Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.
